Joan A. Steitz

Bio: Joan A. Steitz is an academic researcher from Yale University. The author has contributed to research in topics: RNA & RNA splicing. The author has an hindex of 113, co-authored 318 publications receiving 46190 citations. Previous affiliations of Joan A. Steitz include Howard Hughes Medical Institute & Laboratory of Molecular Biology.

Switching from repression to activation: microRNAs can up-regulate translation.

Abstract: AU-rich elements (AREs) and microRNA target sites are conserved sequences in messenger RNA (mRNA) 3' untranslated regions (3'UTRs) that control gene expression posttranscriptionally. Upon cell cycle arrest, the ARE in tumor necrosis factor-alpha (TNFalpha) mRNA is transformed into a translation activation signal, recruiting Argonaute (AGO) and fragile X mental retardation-related protein 1 (FXR1), factors associated with micro-ribonucleoproteins (microRNPs). We show that human microRNA miR369-3 directs association of these proteins with the AREs to activate translation. Furthermore, we document that two well-studied microRNAs-Let-7 and the synthetic microRNA miRcxcr4-likewise induce translation up-regulation of target mRNAs on cell cycle arrest, yet they repress translation in proliferating cells. Thus, activation is a common function of microRNPs on cell cycle arrest. We propose that translation regulation by microRNPs oscillates between repression and activation during the cell cycle.

Target mRNAs are repressed as efficiently by microRNA-binding sites in the 5' UTR as in the 3' UTR.

Abstract: In animals, microRNAs (miRNAs) bind to the 3′ UTRs of their target mRNAs and interfere with translation, although the exact mechanism of inhibition of protein synthesis remains unclear. Functional miRNA-binding sites in the coding regions or 5′ UTRs of endogenous mRNAs have not been identified. We studied the effect of introducing miRNA target sites into the 5′ UTR of luciferase reporter mRNAs containing internal ribosome entry sites (IRESs), so that potential steric hindrance by a microribonucleoprotein complex would not interfere with the initiation of translation. In human HeLa cells, which express endogenous let-7a miRNA, the translational efficiency of these IRES-containing reporters with 5′ let-7 complementary sites from the Caenorhabditis elegans lin-41 3′ UTR was repressed. Similarly, the IRES-containing reporters were translationally repressed when human Ago2 was tethered to either the 5′ or 3′ UTR. Interestingly, the method of DNA transfection affected our ability to observe miRNA-mediated repression. Our results suggest that association with any position on a target mRNA is mechanistically sufficient for a microribonucleoprotein to exert repression of translation at some step downstream of initiation.

A general two-metal-ion mechanism for catalytic RNA

Abstract: A mechanism is proposed for the RNA-catalyzed reactions involved in RNA splicing and RNase P hydrolysis of precursor tRNA. The mechanism postulates that chemical catalysis is facilitated by two divalent metal ions 3.9 A apart, as in phosphoryl transfer reactions catalyzed by protein enzymes, such as the 3',5'-exonuclease of Escherichia coli DNA polymerase I. One metal ion activates the attacking water or sugar hydroxyl, while the other coordinates and stabilizes the oxyanion leaving group. Both ions act as Lewis acids and stabilize the expected pentacovalent transition state. The symmetry of a two-metal-ion catalytic site fits well with the known reaction pathway of group I self-splicing introns and can also be reconciled with emerging data on group II self-splicing introns, the spliceosome, and RNase P. The role of the RNA is to position the two catalytic metal ions and properly orient the substrates via three specific binding sites.

Are snRNPs involved in splicing

Abstract: Discrete, stable small RNA molecules are found in the nuclei of cells1 from a wide variety of eukaryotic organisms2. Many of these small nuclear RNA (snRNA) species, which range in size from about 90 to 220 nucleotides, have been well-characterised biochemically3–6, and some sequenced7,8. However, their function has remained obscure. The most abundant snRNA species exist as a closely related set of RNA–protein complexes called small nuclear ribonucleoproteins (snRNPs)9. snRNPs are the antigens recognised by antibodies from some patients with lupus erythematosus (LE), an autoimmune rheumatic disease10,11. Anti-RNP antibodies from lupus sera selectively precipitate snRNP species containing Ula7 and Ulb9 RNAs from mouse Ehrlich ascites cell nuclei, whereas anti-Sm antibodies bind these snRNPs and four others containing U2 (ref. 8), U4, US and U6 (ref. 9) RNAs. Both antibody systems precipitate the same seven prominent nuclear proteins (molecular weight 12,000–32,000). All molecules of the snRNAs U1, U2, U4, U5 and U6 appear to exist in the form of antigenic snRNPs9. The particles sediment at about 10S and each probably contains a single snRNA molecule. Indirect immunofluorescence studies (refs 12, 13, and unpublished observations) using anti-RNP and anti-Sm sera confirm the nuclear (but non-nucleolar) location of the antigenic snRNPs. Here we present several lines of evidence that suggest a direct involvement of snRNPs in the splicing of hnRNA. Most intriguing is the observation that the nucleotide sequence at the 5′ end of U1 RNA exhibits extensive complementarity to those across splice junctions in hnRNA molecules.

Initial sequencing and analysis of the human genome.

Abstract: The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Efficient in vitro synthesis of biologically active RNA and RNA hybridization probes from plasmids containing a bacteriophage SP6 promoter

Abstract: A simple and efficient method for synthesizing pure single stranded RNAs of virtually any structure is described. This in vitro transcription system is based on the unusually specific RNA synthesis by bacteriophage SP6 RNA polymerase which initiates transcription exclusively at an SP6 promoter. We have constructed convenient cloning vectors that contain an SP6 promoter immediately upstream from a polylinker sequence. Using these SP6 vectors, optimal conditions have been established for in vitro RNA synthesis. The advantages and uses of SP6 derived RNAs as probes for nucleic acid blot and solution hybridizations are demonstrated. We show that single stranded RNA probes of a high specific activity are easy to prepare and can significantly increase the sensitivity of nucleic acid hybridization methods. Furthermore, the SP6 transcription system can be used to prepare RNA substrates for studies on RNA processing (1,5,9) and translation (see accompanying paper).